Design and full-scale experimental evaluation of a seismically endurant steel buckling-restrained brace system

摘要

This paper presents the results of 12 full-scale tests on buckling-restrained brace (BRB) specimens. A simple-to-fabricate all-steel encasing joined by high-strength bolts was used as the buckling-restrainer mechanism. Steel BRBs offer significant energy dissipation capability through nondeteriorating inelastic response of an internal ductile core. However, seismic performance of BRBs is characterized by interaction between several factors. In this experimental study, the effects of core-restrainer interfacial condition, gap size, loading history, bolt spacing, and restraining capacity are evaluated. A simple hinge detail is introduced at the brace ends to reduce the flexural demand on the framing components. Tested specimens with bare steel contact surfaces exhibited satisfactory performance under the American Institute of Steel Construction qualification test protocol. The BRBs with friction-control self-adhesive polymer liners and a graphite-based dry lubricant displayed larger cumulative inelastic ductility under large-amplitude cyclic loading, exceeding current code minimum requirements. The BRB system is also examined under repeated fast-rate seismic deformation history. This system showed significant ductility capacity and remarkable endurance under dynamic loading. Furthermore, performance is qualified under long-duration loading history from subduction zone's megathrust type of earthquake. Predictable and stable performance of the proposed hinge detail was confirmed by the test results. Internally imposed normal thrust on the restrainer is measured using series of instrumented bolts. Weak- and strong-axis buckling responses of the core are examined. Higher post-yield stiffness was achieved when the latter governed, which could be advantageous to the overall seismic response of braced frames incorporating BRBs.